1. Field of the Invention
The present invention relates to display and signal devices and more particularly to display devices with increased luminosity in glare conditions.
Many display devices such as outdoor advertisements, highway signs, obstacle markers, vehicle markers, vehicle instruments and the like must often be read with the observer facing an intense light source such as the sun or oncoming headlights. In these situations the intense light source causes the eyes of the observer to react by narrowing the pupils and initiating protective chemical changes that diminish the capacity of the observer to read and understand any signal close to the incoming light rays. This is the case for example for highway signs on roadways leading in a easterly or westerly direction and travelled in the morning and evening during the winter months. A notorious case is recognized to be the beltway of the Dallas-Fort Worth area where misreading of a single letter can cause long detours for a first-time traveller. In more serious situations where a stop sign or an obstacle is overlooked or an instrument is misread when an observer is unable to see them because they are nearly invisible in contrast with the nearby glare, grave consequences can result. It is the purpose of the present invention to remedy these situations and provide display devices whose signal portion will automatically increase in luminosity when these display devices are viewed in the same field of vision with a glare producing light source.
2. Description of the Prior Art
One way to convey certain messages under glare conditions is to provide highway signs with standardized and distinct silhouettes such as the octogonal stop sign or the triangular yield sign. While such display devices can be discerned by their outline against a glaring light source, the number of messages is limited to a few simple indications. Another way of dealing with the effects of the low sun in traffic signs is shown in U.S. Pat. No. 4,316,652 to Auer. However this traffic signal deals with the effect of the glaring sun when it is behind the observer, whereas the present invention deals with the glare produced when the observer faces a light source head-on. A number of U.S. and foreign patents teach the use of redirected light coming substantially from the overhead sky to illuminate display devices viewed horizontally. By contrast the present invention addresses itself to the problem of display devices viewed on the line of sight with the illuminating light source. The U.S. Pat. No. 2,017,617 to Guistin is cited as an example of how to improve an illuminated display device using the method and apparatus disclosed in this invention. The Guistin street sign differs from the present invention in at least 4 important aspects: (1) it is expressly designed to function not in glare conditions but in an environment lacking sufficient illumination; (2) accordingly it lacks a light concentrator to focus sufficient light onto its name plate, in effect it diffuses light in most directions; (3) to favor visibility in dim lighting conditions the Guistin device uses a large bright background surface with dark lettering, whereas the present invention working in conditions of glaring light requires a bright signal portion disposed on a darker background surface; (4) the cited invention does not show the alignment procedure between the moving light source and the observer crucial to enhance the luminosity of the signal portion to overcome glare conditions.
None of the prior art display devices seem to have the brightness enhancing means to make them especially visible alongside an intense light source.